1. Field of the Invention
The present invention relates to a prewired electrical junction box and, more particularly, to a prewired electrical junction box which allows various types of electrical connections to be made by inserting wires without requiring additional actions to make electrical connections.
2. Description of the Prior Art
Junction boxes, used for making electrical connections between various devices, are well established in the art of electrical wiring. They are primarily used for two purposes: making electrical connections between electrical service cables (cables connected to a central electrical service bus, such as a bus contained in an electrical breaker box) and electrical fixtures (e.g., switches, lamps and receptacles); and making electrical connections between primary electrical service cables which connect to an electrical service bus and secondary electrical service cables which distribute electrical service to various local circuits.
The conventional junction box comprises a housing of plastic or galvanized iron. It has cable ports in several of the walls through which pass the electrical cables to be connected. Cables are connected to electrical fixtures by connecting the ends of wires to the electrical fixtures and subsequently connecting the opposite ends of the fixture wires to service cable wires by twisting the wires together and securing them with a screw-type twist connector. Similarly, service cable connections can be made by inserting the cables to be connected into a junction box and connecting their respective wires with twist connectors.
The primary drawbacks of this type of junction box are that it requires the electrician to perform manual connection of the wires with twist connectors, which is a labor-intensive task and that it is easy to make improper (and sometimes dangerous) connections when connecting complex circuits or using inexperienced electrician's helpers.
Furthermore, conventional junction boxes require room for all of the necessary twist connectors and wires. The minimum dimensions of them are such that implementing a "multi-ganged" arrangement (e.g. where two switches or two receptacles are placed next to each other) requires the electrician to purchase a special multi-ganged to fit the arrangement under a standard face plate. Thus, using conventional junction boxes to implement multi-ganged arrangements significantly adds to the electrical contractor's costs.
Several prewired junction boxes which allow electricians to make wiring connections without having to manually twist-connect wires have been disclosed, such as U.S. Pat. Nos. 2,410,287; 2,433,917; 2,920,303; and 3,885,852. These patents disclose systems whereby special modular fixtures are plugged into single-purpose junction boxes, thereby reducing the labor required to implement an electrical circuit.
There are several disadvantages to these prior art devices: first, they require specially constructed fixtures (as opposed to industry-standard fixtures); second, they involve complex manufacturing processes; and third, their functionality is limited to only one operation. For these reasons, they have not found commercial success.
Other, more recent prewired junction boxes include U.S. Pat. Nos. 3,922,478; 4,165,443; and 4,336,418. These patents disclose systems containing electrical busses whereby electrical connections are made by inserting cables and special fixtures into the junction box.
These devices also have drawbacks that have limited their commercial success, including: requiring the use of specially-manufactured fixtures; not providing lateral support to the electrical service cables; and requiring reconfiguration of the internal busses to create many of the desired circuits.
U.S. Pat. No. 4,924,032 discloses a universal junction box with a plurality of internal busses for making all of the standard connections required in conventional electrical wiring. It allows the electrician to connect standard electrical circuits without manipulating the busses and it uses standard electrical fixtures, all without requiring twist connectors. Furthermore, it allows electrical service connections to be made by inserting electrical cables into openings in the box, both making connections with the busses and providing lateral support to the cables.
However, the '032 device connects the service cables by clamping onto the exposed conductive metal of the cable wires. It does not have a means to clamp onto the insulation of the cable jacket, therefore the lateral support to the cable is limited. Second, the method of connecting the service cable wires in the '032 structure restricts the electrician to choosing highly conductive (and, therefore, highly expensive) materials, such as copper, for wire conductors. Less expensive aluminum cannot be used because as current passes therethrough, the wire heats up; as it heats up it expands, forcing the connector to expand with it; when it cools down it contracts. However, the connector does not contract with it; therefore, when the wire is cool, it has a poor electrical connection. Third, its internal bus arrangement requires the use of expensive 4-wire cable in implementing a three-way switch; this is a disadvantage because 4-wire cable is more expensive than 3-wire cable and electricians prefer not to have to carry the added bulk of 4-wire cable in addition to the 3-wire cable they normally carry. Fourth, the polygonal shape of the box makes it impossible to connect several boxes together to form a "multi-ganged" arrangement, whereby boxes are placed next together to form dual switches and dual receptacles. Fifth, the arrangement of the busses next to the wall of the box made it so that the metal of energized wires is exposed, thus creating a potential safety hazard. Sixth, the wires are not automatically aligned with their respective busses, thus the electrician is required to perform the alignment task thereby increasing the cost of wiring to the electrical contractor.
As can be seen from the prior art, there exists a long-felt, unsolved need for a prewired junction box capable of safely and economically making all standard electrical connections using conventional, industry-standard fixtures.